...because I also replicate in jquery as needed for validation.
–
user756659Dec 21 '13 at 1:06

Thanks and sorry for missing that. I need to replicate some regexs in jquery as I am using the jquery validation plugin for custom rules. So yes, in this case I am not using php necessarily, but I duplicate the expression in both php and jquery.
–
user756659Dec 21 '13 at 1:08

Javascript can always be disabled by a user, therefore I recommend you also use a server-side solution as a backup ;-)
–
Fred -ii-Dec 21 '13 at 1:08

A valid email address can contain many many more different characters than you're allowing!
–
Joel LDec 21 '13 at 1:15

ahh... never even noticed... seems to do the trick. Regarding the ' I am marking those as invalid... a-z, A-Z, 0-9, underscore, hyphen, and period. Plus this handles subdomains.
–
user756659Dec 21 '13 at 1:13

Yes, the dot should be escaped, but failing to do so opens one to false positives, not false negatives. And the risk of false positives tends to be very low. This is one error people usually get away with.
–
Alan MooreDec 21 '13 at 7:52